The present invention relates generally to optical switches, and more particularly to 3D optical switches using controllable mirrors.
Optical switches are useful in communications networks for routing signals from an incoming channel to an outgoing channel. Often, optical switches have multiple input ports and multiple output ports. Each port contains a fiber optic cable providing a data stream to or receiving a data stream from the switch.
Optical switches are generally configurable, so that an input port may have its data routed to any of multiple output ports. This selective routing is often achieved using a set of mirrors and other optical elements. Generally, light is received from an optical fiber and passes through a set of input optics. The light is reflected using one or more mirrors to a desired output optical fiber, with the light passing through a set of output optics prior to coupling to the output optical fiber. Each of the mirrors is usually finely controlled in order to ensure that the light arrives at the proper output optical fiber with a desired coupling efficiency.
In addition to simply providing a beam to the proper output fiber, the position of the beam on the output fiber is often important as well. In order for the maximum amount of light to enter the output fiber, the beam usually should be coincident with the center axis of the fiber and perpendicular to the surface of the fiber. The angle at which the beam strikes the fiber may be referred to as the pointing angle. The distance between the center axis of the fiber and the point at which the beam is incident on the fiber may be referred to as the offset. Misalignment of the beam on the optics of the output port—in pointing angle, offset, or both—may result in insufficient light being transferred to the fiber for the communications network to function effectively.
Often, the mirrors cannot simply be moved to predetermined positions to couple a particular output port to an input. Due to factors such as temperature, manufacturing tolerances, vibration, age, and other factors, simply moving the mirrors to predetermined positions may not guarantee optimum coupling between input and output ports. Thus, a control system may be used to ensure that the desired coupling between the input and output is achieved. Both the angle of incidence of the light and its position on the fiber may be controlled, in both the azimuth and elevation dimensions. However, generally only a single observable, a measured output power, is available for determining the appropriateness of mirror positions. The availability of only a single observable generally results in changing only one parameter associated with mirror positions at any given time. Use of a process which changes a single parameter associated with beam aiming at a time may result in delays in appropriately adjusting aim of a light beam and could cause the algorithm to get caught at a local maxima instead of the global maxima. Further, implementing changes in the aim of a light beam may result in increasing error if measurement errors occur.